Abstract: Hot-pressed SiC-TiC composites with different densities were hot isostatically pressed in N₂. The possibility of that open pores can be closed was analyzed theoretically and confirmed experimentally. Moreover, the effect of post-HIPping on physical and mechanical properties such as density, strength and fracture toughness was investigated. The results showed that SiC and TiC can be transformed respectively into Si₃N₄ and TiN under high pressure N₂ and high temperature. For the SiC-TiC composites with a density of about 95% by presintering under hot-pressing condition and after nitridation by HIPping under 200MPa in N₂ at 1850℃ for 1 h,the room-temperature strength was increased from 345 MPa to 686 MPa,the fracture toughness was up to 7.9 MPa·m^1/2 and the oxidation resistance was also obviously improved.